采用动态冲击汽车零件材料承载特性分析

根据C-NACP车辆正面偏置碰撞要求,获取车身前端结构碰撞过程中材料的应变速率,发现不同位置存在一定的差异;基于材料动态力学性能测试设备,获取车身结构件材料DP800在不同应变速率下的力学曲线,获取关键参数随应变速率的变化情况,获取变化规律;基于Johnson-Cook应变速率相关的本构模型,对材料的本构模型进行拟合;采用落锤冲击试验,对车身常用的帽型梁结构进行冲击测试;基于HyperWorks建立落锤冲击模型,将材料本构模型作为参数输入模型,对比是否应用应变速率相关本构模型,试验测试与仿真分析之间的差异,以验证分析的可靠性。结果可知：车辆碰撞过程中材料的应变速率差异较大,对性能影响较大;DP800呈现与应变速率的正相关,强度随应变速率增加而增大;延伸率、强塑积则呈现先下降后缓慢上升的趋势;落锤冲击表明,材料具有明显的动力力学特性;采用应变速率相关的本构模型作为参数输入,冲击过程最大载荷、平均载荷及压溃量仿真结果与试验结果误差控制在5%以内,且变化趋势基本一致;为考虑应变速率影响,误差较大,关键误差最大超过了30%;分析结果表明,汽车车身材料表现出明显的应变速率相关特性,在碰撞仿真分析...     

C-NCAP工况下铝合金动态力学与失效特性仿真分析

车用材料在碰撞过程中易发生断裂失效,从而影响部件的能量吸收,断裂失效模拟的准确性会影响整车以及部件的仿真精度。而断裂行为的发生与材料性能以及部件的受力状态直接相关,通过设计不同应力状态下的材料样件,对车用6系铝合金材料的动静态力学性能以及GISSMO失效模型的参数进行测试,并建立适合于工程应用的CAE仿真分析材料卡片,对基于C-NCAP工况下的方管动态压溃试验进行对标分析,从而验证失效模型的精确性。     

基于Gissmo失效模型的6016铝合金板材断裂行为研究及应用

准确预测金属板材在成形过程中的失效行为是当前面临的挑战。许多试验表明,金属材料的断裂失效行为伴随着强烈的应变路径依赖性。Gissmo失效模型采用非线性方式计算损伤积累,考虑材料的应力状态对断裂失效应变临界值的影响,适用于预测金属材料在不同应力状态下的断裂行为。以汽车用6016铝合金板材为研究对象,设计六种反映材料不同应力状态的试样,通过试验结合有限元仿真对标的方法,校准Gissmo失效模型中的参数。将Gissmo失效模型用于预测铝合金板材汽车发动机罩内板在冲压过程的断裂失效问题,并对数值模型计算结果进行试验验证。结果表明,与传统成形极限图相比,Gissmo失效模型的计算结果与试验结果更加吻合,铝合金汽车发动机罩内板样件均未出现裂纹区域,表明Gissmo失效模型适合用于准确预测6016铝合金板材的断裂行为。     

基于J-C模型的GH907高温合金动态本构关系及失效关系

使用万能材料试验机、霍普金森拉杆和霍普金森压杆装置研究了航空发动机机匣材料GH907高温合金在常温下的准静态力学性能及20～400℃下的动态力学性能;基于试验结果,拟合得到Johnson-Cook(J-C)本构模型和失效模型参数,并对试验合金动态压缩过程进行模拟以验证本构模型参数的有效性.结果表明:常温下在0～3000 s-1应变速率范围内拉伸时,试验合金具有明显的应变速率效应,但是压缩时对应变速率不敏感;在20～400℃温度范围内,试验合金的软化效应明显;建立的J-C模型能够较为准确地预测该合金在不同温度和应变速率下的力学行为,试样几何尺寸和最大应力的仿真结果与试验结果的相对误差在2％以内.     

6061-T6铝合金薄板剪切试件设计及动态剪切力学特性分析

车身结构影响了整车的碰撞安全性,其中车身承载部件在碰撞过程中主要表现为剪切失效,因此需要对车身材料的动态剪切力学特性展开研究。为了描述6061-T6铝合金材料在复杂工况下的力学特性,进行了准静态和动态力学性能试验。基于不同应力状态和应变率下铝合金力学性能的测试数据,标定了材料的本构模型和断裂模型参数,并通过对比试验与仿真结果验证了材料参数的准确性。为了实现拉伸试验机开展铝合金薄板剪切试验,设计四种形状的薄板剪切试件,采用数值模拟对比所设计剪切试件的应力及应变分布,并分析不同剪切应变率对6061-T6铝合金材料剪切力学特性的影响规律。结果表明：圆形开口对称试件适用于研究塑性变形阶段的失效断裂,而圆形开口偏置试件适用于研究弹性变形阶段的应力应变关系。在低剪切应变率范围内,6061-T6铝合金无显著的应变率强化效应,然而随着应变率的增加敏感性有所提高。     

硬质聚氨酯泡沫动态压缩本构模型研究及有限元仿真

硬质聚氨酯泡沫常被用于缓冲吸能结构,为了更好地在动态加载场景中对该材料进行设计及仿真,需要对其动态力学性能及本构模型进行研究。文章对硬质聚氨酯泡沫进行中低应变率下的动态压缩试验,并进一步分析了应变率对材料性能的影响;使用Avalle模型建立了描述材料压缩力学行为的本构模型,在模型中引入应变率项并基于试验数据的量化分析结果对模型进行了修正;在ABAQUS有限元软件中输入修正后的Avalle本构模型数据,对硬质聚氨酯泡沫进行冲击仿真。研究结果表明：硬质聚氨酯泡沫应力-应变响应对应变率具有敏感性,修正后的Avalle模型对多种应变率下的试验数据拟合较好,而基于该模型进行的有限元数值仿真在6 m/s及8 m/s的冲击条件下加速度峰值与试验数据误差分别为4.09%以及12.72%,模型可靠性较高。     

材料应变率及拉、压非对称特性对汽车碰撞仿真结果的影响

以汽车前保险杠撞柱为侧，研究了材料的应变率及拉、压非对称特性对于仿真得到的零件变形过程、零件吸能特性以及碰撞力变化的影响。结果发现，材料应变率及拉、压非对称特性对仿真结果影响很大。对于某些特殊金属材料如镁合金，在仿真中必须考虑其材料应变率及拉、压非对称特性。     

面向小偏置碰的轮毂断裂模拟研究

为准确地模拟轮毂的碰撞断裂失效行为,开展了AlSi7(铸铝)材料的断裂力学试验,基于CrachFEM失效准则研究了材料特性参数拟合方法.根据轮毂的准静态和动态试验与仿真对比分析,提出了适用于轮毂断裂模拟的有限元建模规则和材料失效参数调整方法,使轮毂碰撞断裂模式的仿真结果更贴合试验结果.研究结果表明:利用所提建模规则与方...     

GH4169高温合金的动态力学行为及其本构关系

采用材料试验机对GH4169高温合金光滑试样与缺口试样进行应变速率为0.000 1～0.010 0s-1下的室温准静态拉伸试验,再利用分离式霍普金森拉、压杆装置进行温度为20～400℃、应变速率为1×102～4×103 s-1下的动态拉伸、压缩试验,得到准静态和动态下的真应力-真应变曲线与失效应变;根据试验数据,采用分步拟合法确定了Johnson-Cook材料模型和失效模型参数,基于Johnson-Cook模型对动态压缩行为进行模拟,并进行试验验证。结果表明:GH4169高温合金的屈服强度随应变速率的增大而增大,随试验温度的升高而降低,该合金具有应变速率强化效应和温度软化效应;模拟结果与试验结果吻合得较好,真应力-真应变曲线的最大相对误差为5.91%,表明经修正后的Johnson-Cook模型可较好地描述GH4169高温合金的动态力学行为。     

AZ31B镁合金断裂应变与应力三轴度的关系研究

对AZ31B镁合金光滑圆棒和缺口圆棒进行了系列准静态拉伸试验,采用ABAQUS对各试样拉伸过程进行了模拟分析。拟合得到了Johnson-Cook断裂失效模型的部分材料常数,建立了AZ31B镁合金断裂应变与应力三轴度的关系模型。将建立的失效模型输入到ABAQUS中进行仿真模拟,模拟结果与试验结果基本一致,验证了断裂失效模型的正确性。     

CrMnFeCoNi高熵合金拉伸断裂的晶体塑性有限元模拟

CrMnFeCoNi高熵合金的优异力学性能使其具有广阔的工程应用前景。材料力学行为的本构描述对其工程服役行为的安全评估至关重要,但是描述CrMnFeCoNi高熵合金拉伸断裂行为的本构模型少见报道。基于晶体塑性本构模型,利用Cohesive单元在多晶代表性体积单元内部植入含损伤破坏机制的晶界,模拟了CrMnFeCoNi高熵合金在单轴拉伸下的晶间断裂过程。模拟结果与试验所得的应力-应变曲线吻合较好,且能准确描述断裂发生时的应力下降过程,说明采用晶体塑性本构模型与Cohesive本构模型可以有效描述材料的宏观响应行为和断裂失效行为。进一步分析表明：裂纹从应力集中处开始萌生;随着应变的持续增加,裂纹沿着晶界扩展,最终造成断裂;晶粒随机取向对裂纹萌生位置与扩展路径有显著影响,但对宏观拉伸应力-应变曲线几乎没有影响。     

基于衍生式设计的汽车线束支架轻量化建模

汽车轻量化技术能有效降低能耗、减少排放和提升安全性。文中以汽车线束支架建模为例,使用空间尺寸参数对汽车线束支架进行轻量化建模后,在确定设计结构、载荷工况和制造方法的基础上,针对两种不同塑料材料,利用先进的脱胎于迭代式算法的衍生式设计得到轻量化设计结果。衍生式设计的结果在满足力学性能和安全系数范围的同时,质量大大减轻,分别减轻了71.57%和74.38%,表明在设计流程中加入衍生式设计可以实现汽车零件的轻量化创新设计,对现代汽车的轻量化设计具有启迪作用。     

Application of Hot Forming High Strength Steel Parts on Car Body in Side Impact

Lightweight structure is an important method to increase vehicle fuel efficiency.High strength steel is applied for replacing mild steel in automotive structures to decrease thickness of parts for lightweight.However,the lightweight structures must show the improved capability for structural rigidity and crash energy absorption.Advanced high strength steels are attractive materials to achieve higher strength for energy absorption and reduce weight of vehicles.Currently,many research works focus on component level axial crash testing and simulation of high strength steels.However,the effects of high strength steel pans to the impact of auto body are not considered.The goal of this research is to study the application of hot forming high strength steeI(HFHSS)in order to evaluate the potential using in vehicle design for lightweight and passive safety.The performance of HFHSS is investigated by using both experimental and analytical techniques.In particular,the focus is on HFHSS which may have potential to enhance the passive safety for lightweight auto body.Automotive components made of HFHSS and general high strength steel(GHSS)are considered in this study.The material characterization of HFHSS is carried out through material experiments.The finite element method,in conjunction with the validated model is used to simulate the side impact of a car with GHSS and HFHSS parts according to China New Car Assessment Programme(C-NCAP)crash test.The deformation and acceleration characteristics of car body are analyzed and the injuries of an occupant are calculated.The results from the simulation analyses of HFHSS are compared with those of GHSS.The comparison indicates that the HFHSS parts on car body enhance the passive safety for the lightweight car body in side impact.Parts of HFHSS reduce weight of vehicle through thinner thickness offering higher strength of parts.Passive safety of lightweight car body is improved through reduction of crash deformation on car body by the application of HFHSS parts.The experiments and simulation are conducted to the HFHSS parts on auto body.The results demonstrate the feasibility of the application of HFHSS materials on automotive components for improved capability of passive safety and lightweight.     

Damage and failure characterization of 7075 aluminum alloy hot stamping

7000 series high strength aluminum alloys are increasingly used in manufacturing automobile body parts to meet the more stringent demands for automobile lightweight. Hot stamping of 7000 series high strength aluminum alloys is a complex thermal-mechanical coupling process and precise simulation is needed to predict material fracture. To obtain damage model of 7075 aluminum alloy in hot stamping, five different stress triaxiality specimens were designed. The fracture strain, critical strain and average stress triaxiality of different specimens were obtained by the hybrid finite element simulation and experiment (FE-EXP) method. GISSMO model of 7075 aluminum alloy at 400 °C was established. Compared with the experimental results of U-shaped part hot stamping under different lubrication conditions, the calibrated GISSMO model was demonstrated to predict the damage behavior of 7075 aluminum alloy during high temperature deformation accurately.

     

Multidisciplinary design optimization of vehicle instrument panel based on multi-objective genetic algorithm

Typical multidisciplinary design optimization(MDO) has gradually been proposed to balance performances of lightweight, noise, vibration and harshness(NVH) and safety for instrument panel(IP) structure in the automotive development. Nevertheless, plastic constitutive relation of Polypropylene(PP) under different strain rates, has not been taken into consideration in current reliability-based and collaborative IP MDO design. In this paper, based on tensile test under different strain rates, the constitutive relation of Polypropylene material is studied. Impact simulation tests for head and knee bolster are carried out to meet the regulation of FMVSS 201 and FMVSS 208, respectively. NVH analysis is performed to obtain mainly the natural frequencies and corresponding mode shapes, while the crashworthiness analysis is employed to examine the crash behavior of IP structure. With the consideration of lightweight, NVH, head and knee bolster impact performance, design of experiment(DOE), response surface model(RSM), and collaborative optimization(CO) are applied to realize the determined and reliability-based optimizations, respectively. Furthermore, based on multi-objective genetic algorithm(MOGA), the optimal Pareto sets are completed to solve the multi-objective optimization(MOO) problem. The proposed research ensures the smoothness of Pareto set, enhances the ability of engineers to make a comprehensive decision about multi-objectives and choose the optimal design, and improves the quality and efficiency of MDO.     

Material flow stress and failure in multiscale machining titanium alloy Ti-6Al-4V

Titanium Ti-6Al-4V alloy is a typical difficult-to-machine material due to its unique physical and mechanical properties. The material properties of Ti-6Al-4V play an important role in process design and optimization. However, the dynamic mechanical behavior is poorly understood and accurate predictive models have yet to be developed. This work focuses on the dynamic mechanical behavior of machining Ti-6Al-4V beyond the range of strains, strain rates, and temperatures in conventional materials testing. The flow stress characteristics of strain hardening and thermal softening can be predicted by the Johnson–Cook model coupled with the adiabatic condition. The predicted flow stresses at small strains agree very well with those from the split Hopkinson pressure bar (SHPB) tests, while the predicted flow stresses at large strains also agree with the calculated flow stresses based on the cutting tests with a suitable depth of cut. Heat fraction and temperature parameter control the range of thermal softening and the decrease rate of flow stress. The material may exhibit super plasticity at a small depth of cut with a large radius of the cutting edge in micromachining. Strain rate is one important factor for material fracture close to the cutting edge. The failure strain increases linearly with the increase of homologous temperature, while it only increases slightly with the strain rate.     

考虑成形方向的航空铝合金修正本构模型的构建

为了能够准确地反映材料成形方向对其动态力学性能的影响,利用电子万能试验机及分离式霍普金森压杆（SHPB）装置,对航空铝合金7050-T7451板材沿不同成形方向（法向ND,横向TD,轧向RD）取样,并进行准静态加载试验和动态冲击剪切试验。结果表明：成形方向是影响材料准静态和动态力学性能的重要因素之一,在动态冲击剪切过程中,铝合金7050-T7451表现出一定的应变率敏感性和正应变率强化效应。基于材料的成形方向影响规律,构建包含应变率敏感函数项的修正的Johnson-Cook本构模型,并对比验证修正模型与试验数据的结果,证明了修正的、包含应变率函数项的材料本构模型更适用于描述不同成形方向下的材料动态力学性能,该模型能够为建立精确可靠的各向异性材料仿真模型提供数据支持。     

An interval-energy-based method for lifetime assessment of dissimilar lightweight metal welded joints

In consideration of uncertainties of material characteristics and its welding and forming process, an interval strain energy density method for predicting fatigue life of dissimilar lightweight metal welded joints was presented in this paper. Firstly, the mechanical performance parameters and fatigue properties of welded joints with parental material aluminum alloy 5083H111 and 5754 were obtained by experimental work. Based on the interval number approach, the interval relationship between the elastic and plastic strain energy density and fatigue life was constructed, including lower and upper interval bounds. Then, a finite element model of the dissimilar lightweight metal cross welded joint was generated to calculate the stress-strain response curve under cyclic loadings through the non-linear finite element analysis. The predicted lifetime and failure location for the cross welded joint based on the interval strain energy density method agreed well with the tested results.

     

Material characterization of blanked parts in the vicinity of the cut edge using nanoindentation technique and inverse analysis

Sheet metal blanking is widely used in various industrial applications such as automotive and electrical rotating machines. When this process is used, the designer can be faced with several problems introduced by the change of the material state in the vicinity of the cut edge. In general, blanking operations severely affect mechanical and physical properties of blanked parts. To take into account these modifications during the part design, it is important to assess the influence of the process parameters on the resulting material properties. Previous experimental and numerical investigations of blanking process have been carried out, leading to the development and the validation of a finite element model that predicts the shape of the cut edge and state of the material. The study presented in this paper makes use of nanoindentation technique to improve the validation of the previously cited model. To this end, nanoindentation tests were combined with inverse identification technique to approach some of the characteristics of material state like work hardening near its cut edges. Indentation tests were carried out in the vicinity of several parts of cut edges. Based on the corresponding load versus penetration curves, the evolution of the yielding stress resulting from the material work hardening was estimated and compared to the predictions obtained from the numerical simulation of blanking process. These comparisons show good agreement between the measurements and the predictions from finite element model.